This may not be medically correct, but based on what happend with my son, it makes sense to me:

When he was cutting his upper front teeth, he had what we thought was a bad cold for a month. Super runny nose, cough, everything. It makes sense to me that since their little faces are so small and compact, when one part swells (gums), other parts are affected (sinuses). He was making a TON of mucus, and I know he was swallowing a lot of it (he spit up some on occasion). I think swallowing a lot of mucus could definately affect their poopie.

Again, I have no medical proof for this, but it really seems plausible to me.